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.TH PTHREAD_ATTR_SETAFFINITY_NP 3 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
pthread_attr_setaffinity_np, pthread_attr_getaffinity_np \- set/get
CPU affinity attribute in thread attributes object
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" "             /* See feature_test_macros(7) */"
.B #include <pthread.h>
.PP
.BI "int pthread_attr_setaffinity_np(pthread_attr_t *" attr ,
.BI "                   size_t " cpusetsize ", const cpu_set_t *" cpuset );
.BI "int pthread_attr_getaffinity_np(const pthread_attr_t *" attr ,
.BI "                   size_t " cpusetsize ", cpu_set_t *" cpuset );
.PP
Compile and link with \fI\-pthread\fP.
.fi
.SH DESCRIPTION
The
.BR pthread_attr_setaffinity_np ()
function
sets the CPU affinity mask attribute of the
thread attributes object referred to by
.I attr
to the value specified in
.IR cpuset .
This attribute determines the CPU affinity mask
of a thread created using the thread attributes object
.IR attr .
.PP
The
.BR pthread_attr_getaffinity_np ()
function
returns the CPU affinity mask attribute of the thread attributes object
referred to by
.IR attr
in the buffer pointed to by
.IR cpuset .
.PP
The argument
.I cpusetsize
is the length (in bytes) of the buffer pointed to by
.IR cpuset .
Typically, this argument would be specified as
.IR sizeof(cpu_set_t) .
.PP
For more details on CPU affinity masks, see
.BR sched_setaffinity (2).
For a description of a set of macros
that can be used to manipulate and inspect CPU sets, see
.BR CPU_SET (3).
.SH RETURN VALUE
On success, these functions return 0;
on error, they return a nonzero error number.
.SH ERRORS
.TP
.BR EINVAL
.RB ( pthread_attr_setaffinity_np ())
.I cpuset
specified a CPU that was outside the set supported by the kernel.
(The kernel configuration option
.BR CONFIG_NR_CPUS
defines the range of the set supported by the kernel data type
.\" cpumask_t
used to represent CPU sets.)
.\" The raw sched_getaffinity() system call returns the size (in bytes)
.\" of the cpumask_t type.
.TP
.B EINVAL
.RB ( pthread_attr_getaffinity_np ())
A CPU in the affinity mask of the thread attributes object referred to by
.I attr
lies outside the range specified by
.IR cpusetsize
(i.e.,
.IR cpuset / cpusetsize
is too small).
.TP
.B ENOMEM
.RB ( pthread_attr_setaffinity_np ())
Could not allocate memory.
.SH VERSIONS
These functions are provided by glibc since version 2.3.4.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR pthread_attr_setaffinity_np (),
.BR pthread_attr_getaffinity_np ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
These functions are nonstandard GNU extensions;
hence the suffix "_np" (nonportable) in the names.
.SH NOTES
In glibc 2.3.3 only,
versions of these functions were provided that did not have a
.I cpusetsize
argument.
Instead the CPU set size given to the underlying system calls was always
.IR sizeof(cpu_set_t) .
.SH SEE ALSO
.BR sched_setaffinity (2),
.BR pthread_attr_init (3),
.BR pthread_setaffinity_np (3),
.BR cpuset (7),
.BR pthreads (7)
.SH COLOPHON
This page is part of release 5.13 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
